Engineers use compression (also called source coding or source encoding) to reduce the bit rate of digital video. Compression decreases the cost of storing and transmitting video information by converting the information into a lower bit rate form. Decompression (also called decoding) reconstructs a version of the original information from the compressed form. A “codec” is an encoder/decoder system.
Over the last two decades, various video codec standards have been adopted, including the ITU-T H.261, H.262 (MPEG-2 or ISO/IEC 13818-2), H.263 and H.264 (AVC or ISO/IEC 14496-10) standards, the MPEG-1 (ISO/IEC 11172-2) and MPEG-4 Visual (ISO/IEC 14496-2) standards, and the SMPTE 421M standard. More recently, the HEVC standard (ITU-T H.265 or ISO/IEC 23008-2) has been approved. A video codec standard typically defines options for the syntax of an encoded video bitstream, detailing parameters in the bitstream when particular features are used in encoding and decoding. In many cases, a video codec standard also provides details about the decoding operations a decoder should perform to achieve conforming results in decoding. Aside from codec standards, various proprietary codec formats define other options for the syntax of an encoded video bitstream and corresponding decoding operations.
In the January 2013 version of the HEVC standard (see Bross et al., “High Efficiency Video Coding (HEVC) Text Specification Draft 8”, JCTVC-L1003_v34, January 2013), a picture can be partitioned into multiple tiles, which are rectangular regions. When the syntax element tiles_enabled_flag is equal to 1, a picture is constructed of tiles. Tiles define horizontal and vertical boundaries within a picture and are organized within the picture according to tile columns and tile rows. When tiles are used, HEVC bitstream syntax and HEVC decoding processes are structured to eliminate intra-picture prediction dependencies across tile boundaries within the same picture, and to eliminate entropy decoding dependencies across tile boundaries within the same picture. Inter-picture prediction dependencies are not constrained, however, with respect to tile boundaries according to the January 2013 version of the HEVC standard.